1. Field of the Invention
The present invention relates to a measurement apparatus and calculation method that is able to calculate accurate azimuth information by compensating for an attitude error of an earth magnetic sensor using information on an earth magnetic field obtained from a two-axis earth magnetic sensor and an inclinometer.
2. Description of the Related Art
Up to now, significant research has been performed to identify a method and apparatus for calculating azimuth information of a vehicle or a sensor module, which moves in free space, using an earth magnetic sensor, such as a fluxgate. However, since the fluxgate is expensive and large in size, it has been used only for navigation.
Recently, smaller and lower cost earth magnetic sensor modules have been developed. Due in part to developments in micro-electromechanical systems (MEMS) technology, chip-type earth magnetic sensor modules have been developed and used in diverse fields that require the azimuth information. In application fields where the earth magnetic sensor module cannot be leveled, however, accurate azimuth information cannot be obtained through only the earth magnetic sensor.
Generally, an earth magnetic sensor is a device for measuring the strength of the earth magnetic field. An earth magnetic sensor can measure the strength of the accurate magnetic field only in a case that a flux vector of the earth magnetic field is parallel to a vector of a measurement axis of the sensor for measuring the flux vector. In this case, after a two-axis magnetic sensor, in which each axis is orthogonally arranged in accordance with a right-hand rule, is horizontally mounted to form a sensor module, the azimuth angle indicated by the sensor module is calculated using outputs of the two-axis sensor.
If the earth magnetic sensor module cannot be leveled, however, the strength of the earth magnetic field cannot accurately be measured, and the azimuth information may include a significant error. Consequently, an error according to an attitude should be compensated for, and to provide this compensation, an error compensation through a coordinate conversion is performed using a three-axis earth magnetic sensor and an inclinometer for measuring the attitude.
With the development of a small-sized earth magnetic sensor, the attitude error compensation technique is able to expand into application fields such as sports, multimedia, game machine, and the like.
In the case of using the two-axis earth magnetic sensor, due to the problems of a sensor installation space, however, the error cannot be compensated for through only the developed error compensation technique. Thus, the azimuth angle calculated increases the error according to the size of the attitude.